Clearly, the only way to stop the conflict is fight fire with fire.
If the pirates like to pretend they are fishermen ... and secretly hide RPGs on their boats, I think some of the other nations' navy personnel can pretend to be recreational divers ... and secretly hide explosive charges under their oxygen tanks.
If pirates can fight guerrilla warfare where they stay at a distance from other vessels with larger ships then deploy smaller ships to attack when others least expect it, the navies can keep their large ships at a reasonable distance from the ports known to harbor pirates and deploy small ships of "recreational divers" to approach the coast, dive at nighttime and blow holes in the hulls of pirate ships in their own ports when they least expect it.
The pirates will have no more ships to go out and pillage and no one will be the wiser as to who is responsible. Sure, they still have booty from their other missions and will buy new ships ... so you sink those ships as well. Basically you starve their funding until the only thing they can do is hurl stones at passing ships because they can't afford RPGs and AK47s. Much more humane, no pirates get hurt and little violence is involved. If they can be sneaky and involve guerrilla tactics, so should their adversaries.